Previous data generated by the applicants suggest that chronic exposure to drugs of abuse leads to long-lasting perurbations in the functioning of peptidergic stress-regulatory systems in the brain. Evidence in this regard is strongest in the case of extrahypothalamic corticotrophin-releasing factor (CRF) systems. More recently, a second neuropeptide system implicated in stress-regulatory functions, the nociceptin/orphanin FQ (N/OFQ) system, was shown to be stronlgy dysregulated following chronic exposure to drugs of abuse. The pathological status of these peptide systems following chronic drug use may play a critical role in abnormal responsiveness to stress and long-lasting vulnerability to relapse associated with exposure to stressful events. The proposed studies will, therefore, test the hypothesis that chronic, high-dose cocaine exposure leads to abnormally enhanced sensitivity to stress, that this state persists over prolonged periods of abstinence and represents a major factor for vulnerability to relapse. This hypothesis is directly linked to the expectation that these behavioral changes are the result of disruptions produced by chronic cocaine in the functioning of extrahypothalamic CRF and brain N/OFQ peptide systems that can be traced to the presynaptic, postsynaptic, or gene expression level within specific brain sites. To test these hypotheses, alterations in stress sensitivity will be measured at three post-cocaine intervals over a 12-week period at the behavioral and neurobiological level. SPECIFIC AIM 1 will examine whether rats with a history of escalated cocaine self-administration show enhanced sensitivity to acute stress compared to rats with only limited-access self-administration experience or cocaine-naive rats using several tests of altered stress-sensitivity. These include direct measures of susceptibility to relapse induced by acute stress and the exacerbation by stress of reinstatement produced by cocaine-related environmental stimuli, as well as measures of "allostatic load" reflected by stress-induced exacerbation of anxiety-like behavior in two behavioral models of anxiety, the elevated plus maze and defensive burying test. SPECIFIC AIMS 2 and 4 (focusing respectively on extrahypothalamic CRF and the N/OFQ system) will then determine whether relationships exist between behavioral hypersensitivity to stress challenges and specific abnormalities in the functioning of the CRF and N/OFQ stress-regulatory systems. Experiments in SPECIFIC AIMS 3 and 5 will employ site-specific microinjection of pharmacological agents to confirm that specific abnormalities in CRF and N/OFQ functioning are responsible for exacerbated stress responses and vulnerability to relapse identified in Specific Aim 1. In addition to providing essential neurobiological information on the relationship between drug-induced alterations of stress-regulatory systems and their relevance for future addictive behavior, these studies are expected to have important implications for treatment drug development aimed at ameliorating chronic cocaine-induced dysregulation of brain stress systems and reducing relapse risk associated with exposure to stressful events.